1. Field of the Invention
This invention relates to an exhaust gas-purifying device for internal combustion engines, which includes an adsorbing device arranged in an exhaust passage of the engine for adsorbing unburnt fuel components contained in exhaust gases from the engine.
2. Prior Art
A catalytic converter, which is arranged in an exhaust passage of an internal combustion engine for purifying exhaust gases, is not fully activated in a low engine temperature condition, e.g. immediately after the start of the engine. This can result in degraded exhaust emission characteristics due to unburnt fuel components being emitted without being burnt in combustion chambers of the engine.
To solve the problem, an exhaust gas-purifying device has already been proposed by Japanese Provisional Utility Model Publication (Kokai) No. 4-105925, which is comprised of an adsorbing device arranged in an exhaust passage of the engine for adsorbing unburnt fuel components, and a catalytic converter equipped with a heater, which is arranged in the exhaust passage at a location downstream of the adsorbing device.
The adsorbing device arranged in the exhaust passage generally has such operating characteristics that it adsorbs unburnt fuel components when the temperature thereof is low, while it releases or desorbs the unburnt fuel components adsorbed thereby when the temperature thereof rises to a predetermined level. In the proposed conventional exhaust gas-purifying device, however, the timing of start of energization of the heater is set irrespective of expected timing of start of release of the unburnt fuel components from the adsorbing device, and as a result, in some cases, the heater starts to be operated too early. This leaves room for improvement in respect of reduction of the consumption of power of a battery for supplying electric power to the heater.
Further, the conventional exhaust gas-purifying device does not take into account deterioration of the adsorbing device due to aging etc., and hence an aged or deteriorated adsorbing device can be undesirably used in spite of its degraded performance, thereby degrading exhaust emission characteristics of the engine.